1. Field of the Invention
The present invention relates to a light emitting device using an organic light-emitting layer, and more specifically, a light emitting device that includes: a lower electrode layer disposed inside a light-emitting region surrounded by a bank (sealing wall); an organic light-emitting layer provided on the lower electrode layer; and a transparent electrode layer provided on the organic light-emitting layer. Also, the present invention relates to a light emitting device that includes: a transparent electrode layer disposed inside a light-emitting region; an organic light-emitting layer provided on the transparent electrode layer; and a counter electrode layer provided on the organic light-emitting layer.
2. Description of the Related Art
The basic structure of a light emitting device using an organic light-emitting material as an organic light-emitting layer is a multi-layer structure in which two electrode layers, that is, a cathode and an anode are provided with a light-emitting layer interposed therebetween. In this case, in order to emit light from the light-emitting layer to the outside, a transparent electrode layer is used as one electrode layer (anode). When the light-emitting material and the electrode layers form a laminated structure, the light-emitting material and the material forming the cathode are highly active with oxygen or moisture and accordingly are easily oxidized in air. Therefore, the lighting-emitting layer and the cathode are formed in a vacuum through, for example, a sputtering or vapor deposition process. However, in order to perform, for example, the vapor deposition process in a vacuum, a large apparatus is required and a large amount of time is required to remove the air. For this reason, it is being requested to form the light-emitting layer and the electrode layer under air.
JP-A-11-273859 discloses a light emitting device in which an electrode is made by combining an active metal, such as Li, Mg, or Ca, with a metal, such as Ag, Al, or In, or is made by laminating a layer formed of an active metal, such as Li, Mg, or Ca, and a layer formed of a metal, such as Ag, Al, or In. The electrode is formed by a vacuum deposition method or by sputtering the organic material containing powder of a metal, such as Mg or Ag. It is possible to screen-print or apply an organic material containing the metal powder. However, since the diameter of a particle of the metal powder is large, that is, the particle has a diameter of several microns, the surface of the metal powder is uneven. Further, since the organic material exists between the particles of the metal powder, it is difficult to obtain a layer made of only the metal and to form a dense layer. Since it is difficult to form a dense layer, it is difficult to prevent inflow of oxygen or moisture. Thus, external oxygen or moisture easily reaches the light-emitting layer through the metal layer, resulting in oxidization of the light-emitting layer.
In the light emitting device using an organic light-emitting material, a cathode and an anode are formed with the light-emitting layer interposed therebetween. Electrons from the cathode and holes from the anode are injected into the light-emitting layer and the injected electrons and holes are recombined with each other to emit light. In such an injection-type light emitting device, holes and electrons are externally supplied to HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) of a light-emitting material. Because a metal or an inorganic semiconductor has more affinity to electrons than many organic materials, in order to inject electrons into the LUMO of the light-emitting material, it is required to form the cathode to have a low work function.
Organic light-emitting materials are broadly classified into two categories, that is, organic low-molecular light-emitting materials, such as an aluminum quinolinol complex, and organic high-molecular light-emitting materials, such as polyphenylenevinylene. In the case of using the low-molecular light-emitting material, a light-emitting layer is formed by the vacuum deposition method, in which the low-molecular light-emitting material is sublimated in a vacuum state and deposited on a glass substrate. In the case of using the high-molecular light-emitting material, since the high-molecular light-emitting material can be melted, a light-emitting layer is formed by a printing technology, such as, a coating method or an inkjet print method. Therefore, it is possible to reduce the fabricating cost and to use not only a glass substrate but also a plastic sheet as the substrate. However, since the cathode layer is easily oxidized, it needs to be formed using a high vacuum by, for example, the sputtering method or the vapor deposition method, and a method of forming a cathode layer at atmospheric pressure has not yet been established. Therefore, even though it is possible to from the organic light-emitting layer under atmospheric pressure by, for example, a printing technique, due to the electrode layers on both sides of the organic light-emitting layer being formed by, for example, the vacuum deposition method or the sputtering method, it is difficult to form the light-emitting layer and the electrode layers under atmospheric pressure all once. Therefore, after the electrode layers are formed in a vacuum, the light-emitting layer is formed under high atmospheric pressure, or the electrode layers are formed by reducing the atmospheric pressure to vacuum pressure, which requires considerable forming time.
Further, since the material used for the cathode easily oxidizes, it is required to seal the light emitting device so as to prevent oxygen or moisture from entering therein. In the past, for example, after electrodes are formed in a high vacuum, a glass substrate is sealed in the high vacuum by using an adhesive which is impermeable to oxygen and moisture. However, since it is difficult to completely shield the light emitting device from oxygen and moisture by such a method, a method of adhering a substrate to a stainless can filled with an absorbent material has been used. JP-A-2001-68264 discloses a gas barrier laminated member forming a metal oxide film using an organosilicon compound. A technique disclosed in JP-A-2001-68264 forms a deposition film of an organosilicon compound by a low-temperature plasma enhanced chemical vapor deposition. The technique is required to be done in a vacuum.